Candida albicans infections in severely immunocompromized patients are not confined to mucosal surfaces; instead the fungus can invade through epithelial and endothelial layers into the bloodstream and spread to other organs, causing disseminated infections with often fatal outcome. We investigated whether secretion of the C. albicans acid proteinase facilitates invasion into deeper tissues by degrading the subendothelial basement membrane. After cultivation under conditions that induce the secretion of the acid proteinase, C. albicans degraded radioactively metabolically labeled extracellular matrix proteins from a human endothelial cell line. The degradation was inhibited in the presence of pepstatin A, an inhibitor of acid proteinases. Pepstatin A-sensitive degradation of the soluble and immobilized extracellular matrix proteins fibronectin and laminin by proteinase-producing C. albicans was also detected, whereas no degradation was observed when the expression of the acid proteinase was repressed. Our results demonstrate that the C. albicans acid proteinase degrades human subendothelial extracellular matrix; this may be of importance in the penetration of C. albicans into circulation and deep organs.